1. Field of the Invention
The present invention relates generally to the field of precipitation detection. The present invention also relates to the field of precipitation differentiation.
2. Description of the Related Art
With the advent of automated track switching systems in modern day railroad lines, constant monitoring of the condition of the rail system is necessary. In moderate weather conditions, track switching is a relatively easy task. However, heavy precipitation, such as snow or freezing rain, can foul the mechanical function of the switches.
Snow and ice buildup between rails presents a typical problem for rail switches, particularly as the ambient temperature decreases or as snow is compressed between ties and rails. Snow can also build up between the rails as a result of small "ground blizzards" left in the wake of passing trains. Such snow and ice buildup can obstruct and hence disable the mechanical movement required for proper rail switching. Freezing rain can also freeze up and disable rail switches.
Special snow and ice melting equipment is typically used to ensure reliable rail switching operations, providing safe operation of the railroad system. Heaters for example are operated at each switch location to melt snow and ice. These heaters, however, are often operated continuously during the months of cold weather even when present weather conditions pose no threat to reliable rail switching, wasting a tremendous amount of energy. This is particularly so for switches located in remote, barren locations and controlled with centralized command centers. The sensing of weather conditions near railway switching systems is therefore crucial to improving the efficiency and safe operation of the railways.
Various precipitation detection devices may be used to enable and disable snow and ice melting equipment such as a heater near railway switching systems. One such device is an electromechanical device that includes a heated wire-mesh screen positioned over a funneling system. Snow that falls incident upon the heated screen is melted. The water collected from the melting snow then acts as a contact, triggering electronics to indicate the presence of snow.
This wire-mesh screen device, though, suffers many drawbacks. Because the wire-mesh screen device is triggered by water, it unnecessarily enables snow melting equipment in response to the mere detection of rain. Additionally, the detection of precipitation by the wire-mesh screen device is very dependent on the trajectory of snow. In turbulent, multidirectional ground blizzards, for example, many snow flakes go undetected as they do not fall incident upon the screen. A heated wire-mesh screen can also evaporate precipitation as it is melting. With relatively light snow or precipitation, this evaporation prevents the detection of snow by the device.
Because of their limited detection area as determined by the size of the funnel system, wire-mesh screen devices must be placed very close to railroad tracks to ensure detection of ground blizzards. This requires the installation of electrical wiring near the track, making such wiring susceptible to being broken or damaged from maintenance trucks and crews.
Another precipitation detection device uses a pair of electrodes spaced apart by a known distance. Precipitation forms a conductive bridge between the electrodes, triggering an indicator that precipitation is present. These devices, however, unnecessarily enable snow melting equipment as mere rain will trigger the device. These devices also have a fixed and limited measuring volume as the electrodes must be relatively close to one another for precipitation to bridge the gap between the electrodes. Furthermore, precipitation which triggers the device may remain between the electrodes, preventing the device from appropriately disabling a heater when precipitation is no longer present. Debris built up between the electrodes may also prevent accurate triggering of the device depending on whether precipitation is present or not.
An electro-optical device serves as a rain gauge and uses a direct forward scatter technique. This electro-optical device emits a partially coherent light beam to a receiver less than a meter away. Another electro-optical device emits a laser beam to a receiver approximately fifty meters away. For both devices, rain or snow falling through the beam path scatters the light emitted by the devices' source. This scattered light is also referred to as "scintillation." Both devices calculate the amount of precipitation based on the detection of such scintillations over time.
These direct forward scatter devices, however, are subject to stability problems. The devices are susceptible to vibrations that can lead to pointing problems in aligning the light transmitter with the receiver. The devices are also cumbersome for setup and use, particularly where the transmitter and receiver are a good distance away from one another. Although a receiver may be placed less than a meter away from the source of a partially coherent light beam for one device, such a configuration suffers from having a fixed and limited measuring distance and volume for the detection of precipitation.
What is desired is a precipitation detection device that more accurately and reliably indicates the presence of precipitation. What is also desired is a precipitation detection device that can differentiate between types of precipitation, for example between rain and snow. What is further desired is a precipitation detection device that can detect precipitation over various sized measuring volumes. What is still further desired is a precipitation detection device that is relatively more stable and less cumbersome for setup and use.